1. Field of the Invention
This invention relates to bonded abrasive compositions and articles made therefrom, the compositions containing abrasive particles dispersed throughout a smear-resistant and wear-resistant polyurea binder matrix, and to methods of making the compositions and articles.
2. Description of Related Art
Abrasive products comprising a solid or foamed organic polymeric matrix having abrasive granules dispersed throughout and bonded therein are well known and widely used. Typically, the polymeric matrix is composed of either a hard, thermoset resin, such as a catalyzed phenol-formaldehyde, or resilient elastomer, such as a polyurethane or a vulcanized rubber.
Bonded abrasives are to be distinguished from coated abrasives in their construction and mode of operation. Bonded abrasives (e.g., grinding wheels) are three-dimensional structures of binder and abrasive grains which rely upon the continual breakdown and removal of the abrasive grains on the cutting surface to continually present sharp cutting points to the material being ground. Coated abrasives, on the other hand, typically have only a single layer of abrasive grains. See, for example, U.S. Pat. No. 5,011,512, incorporated herein by reference.
When elastomeric binder matrices are used in bonded abrasives they generally produce an abrasive article having some degree of flexibility and resiliency. These abrasive articles typically provide a smoother abrasive action and a finer surface finish than that provided by a bonded abrasive article made with hard, thermoset resin. As a result of this, elastomeric bonded abrasive articles have found a wide range of industrial applications, such as deburring, finishing, and sanding in the metal and wood-working industries. However, often these elastomeric bonded abrasive articles have shown premature loss of abrasive particles and, in some cases, undesirable smearing or transfer of portions of the elastomeric binder to the surface of the workpiece.
Conventional flexible bonded abrasive articles typically employ an elastomeric polyurethane as the binder matrix. The polyurethane binder matrix may be a foam, as disclosed in U.S. Pat. Nos. 4,613,345, 4,459,779, 2,972,527, 3,850,589; UK Patent Specification No. 1,245,373 (published Sep. 8, 1971); or the polyurethane binder may be a solid, as disclosed in U.S. Pat. Nos. 3,982,359, 4,049,396, 4,221,572, and 4,933,373.
While synthetic polymers comprising the reaction product of polyisocyanates and oligomeric aminobenzoic acid esters and amines and processes for their preparation are known, they have not been suggested for use as a binder for bonded abrasive articles. U.S. Pat. No. 4,328,322 describes such polymers and processes. The same is true for the polyurethanes and polyurethane/ureas crosslinked with 2-glyceryl acrylate or 2-glyceryl methacrylate which are disclosed in U.S. Pat. No. 4,786,657. This reference describes the use of high equivalent weight diols and diamines, 2-glyceryl acrylate, diisocyanates, and low equivalent weight glycols and diamines in the production of polyurethanes and polyurethane/ureas. (See also Thermoplastic Elastomers, A Comprehensive Review, edited by N. R. Legge, G. Holden and H. E. Schroeder, Hanser Publishers, New York, 1987, P. 13-46.)
A preferred embodiment of this invention relates to an abrasive disc having a molded, integral, toughened, reinforced thermoplastic backing. Background art relating to integral molded backings include:
British Patent No. 1,549,685 describes a method of making a boreless porous grindstone with a plastic holder by compression or injection molding and relates to vitrified bonded abrasive articles;
U.S. Pat. No. 3,960,516 (Biardi) describes a process for making a grindstone with a plastic support formed by a molding process and also relates to vitrified bonded abrasive articles;
German Patent 3,416,186 describes an elastic support disc onto which synthetic resin containing abrasive minerals are coated;
U.S. Pat. No. 4,088,729 (Sherman) discloses a method of molding a thermoplastic hub onto a thermoset plastic abrasive disc;
U.S. Pat. No. 4,774,788 (Shacham et al.) discloses a method of molding a thermoplastic mounting hub having flanges directly onto a grinding wheel;
U.S. Pat. No. 4,554,765 (Grimes) describes a coated abrasive grinding disc, comprising a thermoplastic material bonded to abrasive material with a thermosetting resin, the disc having an integral mounting provision; and
Assignee's co-pending U.S. patent application Ser. No. 07/811,547 (Stout, et al.) describes a coated abrasive backing comprising a reinforced, toughened thermoplastic backing coated with a thermosetting binder and abrasive grains.
While assignee's U.S. Pat. No. 4,933,373 discloses abrasive products which include an improved elastomeric binder which have commercially acceptable utility in many applications, in certain applications they have been found to be deficient in adequately retaining abrasive particles and to have insufficient wear efficiencies. Thus, an unmet need exists for a smear-resistant bonded abrasive article that has improved retention of abrasive particles and high wear efficiency in many applications, and which can be economically and safely fitted onto a tough backing.